Lemma 2.2 [1]}
Let \(G\)  be a graph, and let \(D \in \operatorname{\operatorname{Div}}(G)\) . Then \(r(D - P ) \ge r(D)-1\)  for all
\(P \in V(G)\) , and if \(r(D) \ge 0\) , then \(r(D - P ) = r(D) - 1\)  for some \(P \in V (G)\) .

